Drying of filamentary materials



United States Patent DRYING 0F FILAMENTARY MATERIALS Charles E. Kip, Montclair, and Harold K. Hughes, Summit, N. 3., assignors to Celanese Corporation of America, New York, N. Y., a corporation of Delaware N 0 Drawing. Application September-16, 1954, Serial No. 456,620

7 Claims. (CL 34-9) This invention relates to the drying of filamentary materials and relates more particularly to the drying of filamentary materials having a basis of organic derivatives of cellulose.

In the manufacture of filamentary materials of organic derivatives of cellulose by the dry spinning process, a solution or dope of the organic derivative of cellulose in a volatile solvent is pumped or otherwise forced through a spinnerette'containing' oneor more spinning apertures into a spinning cabinet- A stream of air or other evaporative medium flows through said spinning cabinet and removes from the filamentary materials the major portion of the solvent contained therein. The filamentary materials are then lubricated and taken up in package form or otherwise treated as desired. In applying this process to the manufacture of filamentary materials from organic derivatives of cellulose having a high degree of substitution, preferred solvents employed for forming the spinning solutions are methylene chloride and mixture of methylene chloride and lower aliphatic alcohols such as methanol, ethanol, normal propanol, isopropanol, normal butanol and isobutanol.

When it is desired to obtain the filamentary materials in the form of tow, the filamentary materials emerging from a plurality of spinning cabinets are assembled and the resultant tow packaged. Alternatively, the tow may be cut into staple fibers which are then packaged. The residual solvent in the filamentary materials leaving the spinning cabinet, which may range to as high as 30 to 40% by Weight, or even more, has an undesirable effect on the properties of the packaged filamentary materials, as by causing the same to coalesce. Attempts to dry the tow to remove the major portion of the residual solvents therefrom, when methylene chloride or mixtures of methylene chloride and lower aliphatic alcohols have been employed as the solvents, by the use of heated air as the drying medium are relatively unsuccessful since, at temperatures that will not harm the filamentary materials, it is found that the drying takes so long as to be commercially uneconomical.

It is an important object of this invention to provide a process for drying organic derivative of cellulose filamentary materials which will be free from the foregoing and other disadvantages.-

A further object of this invention is to provide a process for drying organic derivative of cellulose filamentary materials, containing as residual solvents methylene chloride and mixtures of methylene chloride and lower aliphatic alcohols, in the presence of added water.

A still further object of this invention is to provide a process for drying organic derivatives of cellulose filamentary materials containing as residual solvents methylene chloride and mixtures of methylene chloride and lower aliphatic alcohols in an atmosphere having a high humidity.

Another object of this invention is to provide a process for drying organic derivative of cellulose filamentary ma 2,805,490 Patented Sept. 10, 1957 terials containing as residual solvents methylene chloride and mixtures of methylene chloride and lower aliphatic alcohols, by applying to said filamentary materials water, preferably in the form of an aqueous lubricant emulsion, and thereafter drying the filamentary materials.

Other objects of this invention will be apparent from the following detailed description and claims.

According to this invention, organic derivative of cellulose filamentary materials, containing as residual solvents methylene chloride or mixtures of methylene chloride and lower aliphatic alcohols, are dried in such a manner that water is present during at least the initial stages of the drying. The water may be applied directly to the filamentary materials, or the drying may be carried out in an atmosphere having a. high relative humidity. The presence of the water permits the drying to proceed at a much more rapid rate so that the residual solvent content is reduced to an acceptable level in a relatively short period of time. The presence of the water also reduces the tendency. of the individual filaments to coalesce during the drying process.

According to one aspect of the present invention, organic derivative of cellulose filamentary materials, prepared by the dry spinning process from solutions in methylene chloride or mixtures of methylene chloride and lower aliphatic alcohols and containing such materials as residual solvents, have applied thereto a small quantity of water, preferably in the form of an aqueous lubricant emulsion. The filamentarymaterials that have been so treated are then dried, preferably at elevated tempera tures. It is found that the drying of the filamentary materials to which the water has been applied takes place rapidly, so that after drying for a given period of time the methylene chloride and lower aliphatic alcohol content of the filamentary materials is appreciably lower than after drying for the same period of time the. filamentary materials in the absence of applied water. After drying, the water content of the filamentary materials to which water has been applied before drying, is somewhat higher than when no water is applied before drying, but is usually not so high as to be detrimental. In point of fact, in most cases it is found that the water content of the dried filamentary materials is not above the water content which such filamentary materials would have in equilibrium with the atmosphere at normal conditions of temperature and humidity.

According to another aspect of this invention, organic derivative of cellulose filamentary materials, containing as residual solvents methylene chloride or mixtures of methylene chloride and lower aliphatic alcohols, are dried at an elevated temperature under conditions of high humidity. Such high humidity drying conditions may be maintained throughout the entire drying process, or may he maintained only during the initial portions of such process. Organic derivative of cellulose filamentary materials that have been dried in this manner have a much lower content of methylene chloride than filamentary materials that have been dried under low humidity conditions.

The best results are obtained when the process for the drying of the organic derivative of cellulose filamentary materials includes as an initial step the application to the filamentary materials of a small proportion of water, followed by drying the said filamentary materials at an elevated temperature under conditions of high humidity.

While the process of this invention is generally applicable to the treatment of any organic derivative of cellulose filamentary materials containing as residual solvents methylene chloride and mixtures of methylene chloride and lower aliphatic alcohols, it is especially useful in the drying of such filamentary materials when the organic supporting the filamentary materials. operation, the drying apparatus should be of the continuof cellulose filamentary materials to be treated in accordance with this invention may range up to about 40% by weight, or in unusual cases, even more, and will normally lie in the range of between about 15 and 25% by weight. When the filamentary materials have been spun from solution in a mixture of methylene chloride and lower aliphatic alcohol, the methylene chloride in the residual solvent comprises between about 60 to 95% by weight of the total residual solvent. The major portion of the remainder of the residual solvent is the lower aliphatie alcohol.

The filamentary material containing such residual solvents have applied thereto a small proportion of water, preferably in the form of an aqueous lubricant emulsion. The application of the water to the filamentary materials may take place after the said filamentary materials have traversed the major portion of the spinning cabinet in which they are formed, or after they have emerged from such spinning cabinet. The quantity of water applied to the filamentary materials may range from about 2 to 25 by weight, based on the solvent free weight of the said materials. As stated above it is preferred to apply the water to the filamentary materials together with a lubricant in the form of an aqueous lubricant emulsion, of which many are known in the art. In this way it is possible to apply the water to the filamentary materials without adding an extra step to the process of manufacturing the filamentary materials.

Following the application of the Water thereto, the filamentary materials are dried at an elevated temperature of between about 65 C. and a temperature which will degrade the filamentary materials, as by causing the filaments therein to fragment or to coalesce. For filamentary materials of cellulose acetate containing fewer than about 0.2 free hydroxyl groups per anhydroglucose unit in the cellulose molecule, preferred drying temperatures are between about 65 and 100 C. The duration of the drying cycle under these conditions is between about 1 and minutes, which is commercially economical. During the drying, a stream of heated air is circulated over the filamentary materials to assist in removing the solvent vapors from the vicinity of the filamentary materials thereby to increase the speed of drying. The solvent vapors in this stream of air may be recovered for reuse in a manner well known in the art.

Any suitable form of apparatus may be employed for carrying out the drying, so long as it permits the desired temperatures to be reached and provides for the movement of the air therethrough. The drying apparatus should also be equipped with means, such as a belt, for For commercial ous type in which the filamentary materials are entered into said apparatus continuously, pass through said apparatus, and are removed continuously from said apparatus in a dried state.

Whether or not water is applied to the filamentary .materials prior to the drying thereof, the speed of drying may be increased by carrying out the drying at an elevated temperature under conditions of high humidity.

'When drying the filamentary materials in this manner,

the temperatures employed are those specified above and sufiicient moisture is added to the air to bring its relative humidity to at least about or preferably to at least about It is not necessary to hold the humidity high throughout the entire drying process, an improvement in the speed of drying being obtainable when only the initial portion of the drying is carried out at high humidity, particularly when the relative humidity during such portion exceeds about 15%. In such case, the duration of the initial portion of the drying should constitute at least about 10% of the total drying cycle. The drying of the filamentary materials under conditions of high humidity also reduces the tendency of the filaments to coalesce one with the other during the drying cycle. Any

suitable expedient may be employed to increase the humidity during the drying. For example, steam or water may be sprayed into the drying air or the drying air may be forced through a water bath before being A 360,000 denier tow of 3.75 denier cellulose acetate filaments in which the cellulose acetate has an acetyl value of 59.5%, calculated as acetic acid, is spun from a solution of said cellulose acetate in a mixture of methylene chloride and methanol. The freshly spun tow contains 11.4 weight percent of methylene chloride, 3.3

weight percent of methanol, and 0.2 weight percent of water. The said tow is dried for seconds in air saturated with steam at atmospheric pressure and is then dried for an additional 3 minutes and 30 seconds in air heated to 80 C. and having a relative humidity of.5%.

'After the drying, the tow contains 2.2 weight percent of methylene chloride, 0.3 weight percent of methanol and 1.3 weight percent of water. When the same tow is dried for .4 minutes in air heated to C. and having relative humidity of 5%, the dried tow contains 2.8 weight percent of methylene chloride, 0.6 weight percent of methanol and 0.5 weight percent of water. An examination of the dried tow under a microscope shows bad coalescence. of the filaments in the tow dried under conditions of low humidity throughout, but only slight coalescence of the tow in which the initial portion of the drying is carried out under conditions of high humidity. The decrease in the residual solvent content of the tow when a portion of the drying is carried out under conditions of high humidity, decreases the possibility that the filaments in the tow will coalesce or that the tow will be otherwise damaged during its subsequent processing.

Example II at 80 C. in air having a relative humidity of 5%. The

dried tow has a methylene chloride content of 2.1%

by weight, a methanol content of 1.2% by weight and a water content of 3.1% by weight. When the water application is omitted and the tow is dried under the same conditions in other respects, the dried tow has a methylene chloride content of 2.3% by weight, a methanol content of 1.8% by weight and water content of 2.6% by weight.

Example III A 360,000 denier tow of 3.75 denier cellulose acetate filaments in which the cellulose acetate has an acetyl value of 59.5%, calculated as acetic acid, is spun from a solution of said cellulose acetate in a mixture of methylene chloride and methanol. The freshly spun tow has a residual solvent content of 11.7 weight percent methylene chloride, 4.3 weight percent methanol and 0.9 weight percent water. The freshly spun tow is lubricated with a suificient quantity of an aqueous lubricant emulsion so that 34% by Weight of water is applied to the tow. The tow is then dried for 4 minutes at 80 C. in air having a relative humidity of 5%. The dried tow has a residual solvent content of 2.1 weight percent methylene chloride, 1.9 Weight percent methanol and 2.6 weight percent water. When the tow is lubricated with the same lubricant as a whole oil rather than as an aqueous emulsion and then dried under the same conditions, the dried tow has a residual solvent content of 4.8 weight percent methylene chloride, 4.0 weight percent methanol and 0.7 weight percent water.

Example IV A 360,000 denier tow of 3.75 denier cellulose acetate filaments in which the cellulose acetate has an acetyl value of 61.5% calculated as acetic acid, is spun from a solution of said cellulose acetate in methylene chloride and methanol. The freshly spun tow has a residual solvent content of 5.9 weight percent methylene chloride, 3.9 weight percent methanol and a small amount of water. The said tow is dried for 4 minutes at 80 C. in air to which suflicient water has been added to bring its relative humidity to 23%. The dried tow has a residual solvent content of 2.7 weight percent methylene chloride, 3.6 weight percent of methanol and 2.7 weight percent of water. When the drying conditions are changed by reducing the relative humidity of the air to 5%, the dried tow has a residual solvent content of 5.4 weight percent of methylene chloride, 3.2 weight percent of methanol, and 1.4 weight percent of water.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein fthout departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for drying organic derivative of cellulose filamentary material containing as residual solvents materials of the class consisting of methylene chloride and mixtures of methylene chloride and lower aliphatic alcohols, which comprises drying the filamentary material, at a temperature of between about C. and the temperature at which the filamentary material will degrade, in an atmosphere having a relative humidity of at least about 15%.

2. Process as set forth in claim 1 in which said high relative humidity is due to the presence of applied water on said filamentary material.

3. Process as set forth in claim 2 in which an aqueous lubricant emulsion is applied to said filamentary material before said drying, so as to cause the air in the neighborhood of said filamentary material to have said high humidity during said drying.

4. Process as set forth in claim 1 in which a current of air having a temperature of 65 to C. is passed over said filamentary material during said drying.

5. Process as set forth in claim 1 in which said filamentary material is cellulose acetate containing fewer than about 0.2 free hydroxyl groups per anhydroglucose unit in the cellulose molecule.

6. Process as set forth in claim 5 and in which a current of hot air having a temperature of 65 to 100 C. is passed over said filamentary material, said filamentary material before drying containing at least about 15% of said residual solvents.

7. Process as set forth in claim 6 in which said hot air is prehumidified to said relative humidity of at least 15% before it is passed over said filamentary material, said process including a further drying of said filamentary material at said temperature under conditions of lower humidity.

References Cited in the file of this patent UNITED STATES PATENTS 2,161,354 Imray et. al June 6, 1939 2,557,993 Oliver June 26, 1951 FOREIGN PATENTS 434,320 Great Britain Aug. 29, 1935 

1. PROCESS FOR DRYING ORGANIC DERIVATIVE OF CELLULOSE FILAMENTARY MATERIAL CONTAINING AS RESIDUAL SOLVENTS MATERIALS OF THE CLASS CONSISTING OF METHYLENE CHLORIDE AND MIXTURES OF METHYLENE CHLORIDE AND LOWER ALIPHATIC ALCOHOLS, WHICH COMPRISES DRYING THE FILAMENTARY MATERIAL, AT A TEMPERATURE OF BETWEEN ABOUT 65*C. AND THE TEMPERATURE AT WHICH THE FILAMENTARY MATERIAL WILL DEGRADE, IN AN ATMOSPHERE HAVING A RELATIVE HUMIDITY OF AT LEAST ABOUT 15%. 